Powder Coating Basics

Written
by
Norbert Poole
on August 29, 2007 Powdercoating Is More Durable Than Paint And Can Be Applied To Anything Made Of Metal. Here Are Some Tips And Tricks On What Powdercoating Is And How To Get Stuff Coated.

There are three basic ways to make a car and/or its parts look good: painting, plating, and powdercoating. Since we just finished our huge, 10-part series on how to paint your car last month, this month, we'll touch on what powdercoating is all about.

Powder Coating ExplainedWhy is it called powdercoating? To put it simply, the coating is originally applied as a thermosetting powder made up of polyester, epoxy, and acrylic resin combined with various crosslinking compounds. The powder is so fine that each grain looks like a piece of dust, and you can order powder in thousands of different colors and textures for very specific applications. The powder is usually either sprayed on the part or the part is passed through a booth filled with powder (used most often in mass-production powdercoating).

The powder is usually applied to the component by applying a low-voltage electrical charge to both the part and the plastic particles-but the charges are opposite, so the powder is attracted to the surface of the part. This way, the powder need only be sprayed in the general area of the part for it to evenly coat it. On intricate components, this can create some issues, but the better powdercoaters (such as Cooter's Powder Coating in Grand Blanc, Michigan, which we used for much of the information in this story) have methods to provide an even coating on complex surfaces.

After a part is sprayed, it is transferred to a large oven heated to between 350 and 400 degrees F. It is left there until it attains a temperature at which the powder "melts" and flows into a smooth, extremely durable coating. The heat also causes the powder to chemically react in a process called crosslinking, which is what makes it so durable.

The solvent emissions with powdercoating are also very low compared with spray painting, so powdercoating is more ecologically friendly. Also, powdercoating is much more resistant to solvents, blunt-object impacts, and other issues that would damage paint. Sounds good, right?

Prepping For PowderAs with painting a car, the application of the powder is the easy part; the real work is in the prep. Before coating, thoroughly disassemble the part to its basic level and then clean it of any paint, grease, rust, or other materials that would prevent good adhesion of the powdercoating to the parent material. This teardown should include materials that can't handle the heat of the oven, like rubber, tape, and plastic. This level of disassembly isn't much different from prepping for paint; it's just the extreme end of the prep spectrum. Usually, the best way to ensure a clean surface is to blast the part with sand or another medium.

Since the blasting material will get into everything, you must remove all threaded or lubricated interfaces, like bearings, sealed surfaces, bolts/nuts, clamps, and the like, as these will be crunchy junk after blasting. If you're blasting suspension parts, you'll have to replace stuff like A-arm bushings, as they are usually destroyed when you remove them, but that's the price you pay to look good for a long time. Another process sometimes used to clean parts is chemical stripping. Where blasting is good for parts that have intricate shapes, dipping is better for sheetmetal panels because blasting generates heat that can warp sheetmetal. A phosphate bath is recommended to prevent the sheetmetal from being continually attacked by the chemicals after the process is completed (leading to rusting of the very sheetmetal you are trying to protect). Immediately before powdercoating, the parts are wiped down with solvent and a lint-free rag and placed on a hanger to allow coating on every possible surface.

When looking for a powdercoating shop, it's best to rely on experience and specialization that fit your needs. For instance, Cooter's has developed its business to specialize in coating one-off-style hot-rod parts instead of high-volume pieces. With that in mind, the company has developed a series of special systems and processes, including an oversized oven that's equipped with almost 24 thermocouples to carefully control the heat being applied to everything from bolts to complete chassis. The oven is operated via an advanced, Cooter's-designed oven controller that is able to read part temperatures (the critical component in powdercoating) practically anywhere in the oven.

What's so cool about powdercoating? It is one of the best looking, most durable, ecologically responsible, and cost-effective methods of coating metal parts. As with most final steps, the details define the final look, so the parts being powdercoated will need to be completely disassembled, stripped, and then the color selected. But it'll all be worth it once you get the car assembled.

Do-It-Yourself Powder CoatingIt is possible to do your own powdercoating at home using Eastwood's HotCoat Powder Coating systems. The HotCoat line includes everything from a kit with just an entry-level powder gun up to a fully equipped kit with a professional-level applicator gun, powder, surface-prep chemicals, protective plugs, and more. You'll need to supply an electric oven or toaster oven (but don't put food in it afterward) and a ventilator mask, but otherwise, you'll be ready to start coating. For more details, check out the Eastwood Web site (eastwood.com) and click on the HotCoat Powder Coating tab. Eastwood also has a good beginner-level video showing what it looks like to powdercoat a part like a valve cover. You can order via the Web site or call 800/343-9353.

Chassis Powder Coating SecretsOne of the more challenging yet rewarding powdercoating applications is a complete vehicle chassis. The powdercoater needs to be able to handle the oversized, heavy chassis during the surface prep, fixturing, powder application, and oven-curing steps, which not all shops can do. Cooter's Powder Coating has designed and built all of its systems to handle full chassis with the thought that if the company can handle these oversized components, it can handle anything.

Top 3 Powder Coating Prep Tips1. Remove anything not intended to be powdercoated. Besides removing stuff you don't want coated, since powdercoating involves time in an oven near 400 degrees F, you'll want to remove anything plastic or rubber, bearings, plated components, or other temperature-sensitive pieces.

2. Account for the thickness of the powdercoating. When powdercoating a component that interfaces with another part, like a mounting bracket or suspension component, you need to take into account the additional thickness of the powdercoating. The thickness of powdercoating usually varies between 1 and 3 mils (about the thickness of a garbage bag), so make sure to add that into the clearances required.

3. Cover areas that shouldn't be coated. Make sure the powdercoater puts plugs in threaded holes, holes where fasteners pass through, and any other holes into which you don't want powdercoating to go. High-temperature tape is placed over larger areas that need to remain bare metal, like an engine-block cylinder-head mounting surface.

Types Of Powder MaterialsAlthough there are several different powder formulations used by the powdercoating industry, three types of powder are predominantly used to coat automotive components.

Standard polyester: Standard polyester is an all-around powder for indoor and outdoor use and was one of the first formulated powders that coaters used for automotive applications-it is also the most economical powder to spray.

Enhanced polyester: This has better durability and film-appearance characteristics, applies a little smoother than standard polyester, and has a greater chemical-resistance level than standard polyester.

Super polyester: Super polyester is the cutting edge of powders available today. In automotive applications, it is very durable against impact and UV exposure and has a much higher chemical resistance (to things like paint-attacking brake fluid). Super is usually a requirement on components like wheels on production cars.

We'd suggest using enhanced or super, considering you're coating parts on your pride and joy-and the price and prep difference is mild compared with the properties of these two powders. All three powders can be ordered as low-cure (which means they flow out at around 400 degrees F) for use on temperature-sensitive automotive parts. As an added bonus, all powders are now ordered with an industry-standard numbering system called a "ral" number for the color. For example, ral 5008 = blue gray. This will make it much easier to shop for a powdercoater, as you'll be able to pick your color and get the ral number for it, along with the powder type (standard, enhanced, or super polyester) so you can easily compare the quality, timeliness, and price of coating among powdercoaters.

Sample Costs For Powder CoatingNote: Prices go up dramatically depending on the amount of prep work (blasting, sanding, and so on), coats of powder, type of powder used, and if a part has powdercoating on it that needs to be either burned off or chemically removed.